Starting materials based on rare sugars that are used in the production of carbohydrate-based drugs are in low supply, therefore creating high prices. One such carbohydrate is L-ribose. L-Ribose is used in many different applications, including several nucleoside-based Pharmaceuticals presently available or undergoing clinical trials. As the need for these drugs increases, demand for L-ribose is going to increase significantly. This proposal outlines a new synthetic route to L-ribose production, which will result in lower-cost of manufacture than the current state-of-the-art. The technologies developed for the L-ribose production can then be translated into the production of other rare sugars to expand the portfolio of carbohydrate starting materials available to biochemists and synthetic carbohydrate chemists. The proposed route to L-ribose utilizes an enzymatic process. To achieve large-scale production of L-ribose a eukaryotic gene will be synthetically constructed to express in a microbial host. Initially, Escherichia coli and Saccharomyces cerevisiae will be tested as a suitable production system. This synthetic route has several potential advantages over the current commercial routes by using a single-step fermentation from a readily available starting material. Phase I of this proposal would study the gene expression within a heterologous expression strain. The goal of the phase I portion of the proposal is to produce an active gene within an expression host and improve the activity with directed evolution. The specific aims of this Phase I grant are 1) to construct and express the specific gene; 2) Assay development; and 3) Preliminary engineering of enzyme activity. By developing this advanced production of rare sugars used by the pharmaceutical industry and other research institutions, the public will have access to better and cheaper treatments for disease.